The following code is working perfect, it is added into "report.external_layout_footer", it selects a footer message to print only in the invoices.

<t t-if="'type' in o.fields_get()"> <div class="text-center" style="border-top: 1px solid black;font-size:0.7em"> Autorizado mediante resolución #11-97 del 12 Agosto de 1997, de la D.G.T.D </div> </t>

However in "general settings"  in the option: "Preview External Report"  I get a compiling  error as follows:

Error to render compiling AST
AttributeError: 'NoneType' object has no attribute 'fields_get'
Template: report.external_layout_footer
Path: /templates/t/div/t
Node: <t t-if="'type' in o.fields_get()">
        <div class="text-center" style="font-size:0.7em" data-oe-id="272" data-oe-model="ir.ui.view" data-oe-field="arch" data-oe-xpath="/t[1]/div[1]/t[1]/div[1]"> Esta factura devengar&#225; un 4% de inter&#233;s mensual despu&#233;s de su vencimiento, de acuerdo al art&#237;culo 460 del C&#243;digo de Comercio. Esta factura constituye titulo ejecutivo. </div>
        </t>

Any idea why  why this happen,  printing invoices and other reports I do not get any error, only when I try to Peview External Report as explained above.

I will appreciate and tip why this happens.

Thanks

LS